A common problem encountered with natural and synthetic materials, particularly synthetic organic polymers, is instability on exposure to light, atmospheric conditions and elevated temperatures, as well as the adverse effects exerted on the polymers by the minute amounts of catalyst residues often present in the synthetic polymers, which frequently lead to physical deterioration and color change. Over the years industry has resorted to the addition of a wide variety of antioxidants, ultraviolet light absorbers and heat stabilizing agents to the polymers but it still exerts a continuing effort to find new materials that will accomplish the same or improved objectives without affecting other properties that may have a deleterious effect on subsequent manufacturing and processing operations. It is also known in industry that a compound that stabilizes against heat and/or oxygen degradation may not stabilize against light degradation in the same material, and vice versa. It is further known that a compound which exerts some form of stabilization in one type of material may be completely ineffective in another type of material. Thus, compounds are classified as antioxidants, light stabilizers, heat stabilizers, etc., depending upon the stabilizing effect a particular compound may have on a specific material or type of material. Further, in many cases, mixtures of stabilizers are used to obtain desired protection against one or more forms of degradation.
It is also known that residues from the polymerization of alpha-olefin polymers using transition metal catalysts, such as the Ziegler and Natta type catalysts, show adverse effects on both stability and product color. In order to off-set the adverse effects caused by the catalyst residues increased amounts of stabilizers have been required. The adverse effects result, in part, from the reaction of the transition metal residues of the catalysts with the conventional hindered phenolic antioxidants employed or their breakdown products as the antioxidants act as radical terminators. The halide or chloride residues of the catalysts can react with the conventional hindered phenolic antioxidants catalyzing its dealkylation and promoting the autooxidation. Further, phenolate salts or coordination complexes can form that are chromophores. This is especially easy with the acid catalyzed dealkylation of the conventional hindered phenolic antioxidants.
A common widely used commercial practice has been the addition of metallic stearates of zinc, magnesium, and/or calcium as acid acceptors with the conventional hindered phenolic antioxidants. However, the use of metallic stearates can cause plate-out or die lip build-up problem, and they often interfere with heat sealing and ink adhesion. Ultrafine zinc oxide or hydrotalcite ( a hydrate of magnesium carbonate/aluminum hydroxide) can be used to replace the metal stearates in some instances, however, these inorganic materials often show dispersion problems. Such inorganic materials by themselves or when wetted with small amounts of metal stearates are not effective in controlling discoloration but show a positive effect on reducing corrosivity.
Another practice, often used to further improve color and stability during melt processing, is the addition of phosphite ester derived from nonylphenol or 2,4-di-t-butylphenol.
It has now been found that a novel class of polysiloxanes having pendant sterically hindered phenol moieties connected to the silicon atom via a carbonyloxy-containing link stabilize synthetic polymers against the deleterious effect caused by exposure to atmospheric conditions.
Polysiloxanes containing t-butyl substituted phenyl groups have been known for many years. Thus, U.S. Pat. No. 3,328,350, issued June 27, 1967 to G. M. Omietanski et al., discloses polysiloxanes of superior stability towards oxidative degradation which are the reaction products of selected substituted phenols with acyloxy terminated polysiloxanes. The final product contains the phenyl group in the polymer chain and it is not a pendant group.
In U.S. Pat. No. 3,328,450, issued June 27, 1967 to E. P. Plueddemann, there are disclosed alkyl phenol-substituted organosilicon compounds and polysiloxanes containing such compounds. However, none of the compounds disclosed contain a pendant sterically hindered phenol moiety connected to the silicon atom via a carbonyloxy-containing link.
The disclosure in U.S. Pat. No. 3,579,467, issued May 18, 1971 to E. D. Brown, also disclosed polysiloxanes containing a phenol moiety. However, the phenol moiety is not connected to the silicon atom via a carbonyloxy-containing link.
In U.S. Pat. No. 4,430,235, issued Feb. 7, 1984 to N. S. Chu et al., polymeric siloxane antioxidants are disclosed that contain an antioxidant moiety, for example, a hindered phenolic group. However, the reference does not suggest or disclose any compound in which the phenolic moiety is connected to the silicon atom via a carbonyloxy-containing link.
U.S. Pat. No. 4,535,113, issued Aug. 13, 1985 to G. N. Foster, et al., discloses olefin polymer compositions containing silicone additives. The siloxane additives, however, are not those described in the instant invention.
The invention described in U.S. Pat. No. 4,645,844, issued Feb. 24, 1987 to A. Berger et al., discloses phenoxy containing silane compounds wherein the phenoxy group is attached to the silicon atom via a methylene or alkylene link and nowhere suggests or discloses a connection via a carbonyloxy-containing link.
A number of abstracts in CA Selects Organosilicon Chemistry disclose a variety of phenol-substituted silanes useful as antioxidants, however, none of them disclose or suggest the compounds of this invention. (See: the silane of Issue 8, 1986, page 14, abstract 131201e; the disiloxane of Issue 9, 1986, page 21, abstract 150606g; the disiloxane of Issue 10, 1986, page 10, abstract 169116u; the silane of Issue 14, 1986, page 11, abstract 7394b; and the silane of Issue 17, 1986, page 12, abstract 61488y.)
It has now been found that certain polydialkylsiloxanes containing siloxy units having defined pendant sterically hindered phenol moieties connected to silicon atom of the siloxy units via a carbonyloxy-containing link, alone or in combination with other stabilizers, stabilize synthetic olefin polymers against the deleterious effect caused by exposure to light, heat and metal catalyst residues.